The present invention relates to a control apparatus for an electric vehicle and a method thereof for controlling a dc motor for driving the electric vehicle, and in particular, it relates to a braking control of the electric vehicle.
It is known in order to shorten a transition period of time when switching from a regenerative braking mode to a plugging braking mode in an electric vehicle that immediately after detection of a make-contact of a regenerative contactor, a chopper operation for reverse braking is started. It is disclosed in JPA No. 7-46707 that when switching from a regenerative braking to a plugging braking by reading a contact voltage of a regenerative contactor, a main transistor is caused to be on for a minimum period of time during a delay time until the regenerative contactor is closed, and a make contact of the regenerative contactor is detected on the basis of a contact voltage of the regenerative contactor, then a shift to the plugging brake mode is enabled.
In the steps of the aforementioned prior art, it is inevitable when shifting from regenerative braking to plugging braking to stop its regenerative braking once before execution of a regenerative contactor make-contact control, after execution thereof and during a delay time until the regenerative contactor is closed, a main transistor is switched on for a minimum period of time, then the make-contact of the regenerative contactor is detected. Therefore, during the delay time of several tens ms until make-contact of the regenerative contactor, because the main transistor is switched on for the minimum period of time, almost no current conduction state (if any, for a very limited period of time) exists in the motor. During this period of time of no current conduction states in the motor, no braking torque is generated thereby allowing the vehicle to cruise. This period of time without generation of braking torque during transition from regenerative braking to plugging braking is felt by the driver as a switching lag time to deteriorate the feeling during switching therebetween.
Further, although description of detection of the contact voltage of the regenerative contactor is given in the prior art, no consideration is given to a case when the contact voltage of the regenerative contactor cannot be detected due to a failure of wiring or the like.